PROJECT SUMMARY & ABSTRACT Human locomotion through natural environments requires the coordination of all levels of the sensorimotor hierarchy, from the cortical areas involved in processing of visual information and high level planning to the subcortical and spinal structures involved in the regulation of the gait and posture. However, despite the complex neural bases of human locomotion, the output is highly regular and well organized around the basic physical dynamics and biomechanics that define the stability and energetic costs of moving a bipedal body through space. There is a rich and growing body of literature describing detailed knowledge each of the individual components of human locomotion, including neural mechanisms, muscular neuromechanics, and biomechanics. However, very little research exists on the way that visual input is used to dynamically control locomotion, and the overall control structure of the integrated neural and mechanical system during natural locomotion through a complex and dynamic world. This lack of integrative research not only restricts the breadth of impact of research from these individual disciplines, but also limits our ability to develop adequate treatment plans for loss of locomotor ability deriving from systems-level factors such as aging, stroke, and Parkinson?s disease. In order to to fill this critical gap in our knowledge about human locomotion, it is necessary to develop an integrated research program that examines the interactions between the visual, neural, and mechanical bases of human movement through the world. In service of this general goal, this proposal outlines research projects aimed at specific unanswered questions about locomotion over different terrains. This proposal comprises three specific research and training aims on the visual control of locomotion over rough terrain. Aim 1 focuses on the behavioral task itself, Aim 2 investigates the sensory stimulus experienced during real-world locomotion, and Aim 3 examines the motor integration of visually specified goals into the ongoing gait cycle. Aim 1 investigates effects of changing environmental uncertainty and task demands on gaze allocation strategies during locomotion over real-world rough terrain. Aim 2 analyzes and models the visual stimulus experienced during locomotion over real-world rough terrain. Aim 3 determines how visually specified target footholds and targets are integrated into the ongoing preferred steady-state gait. Together these aims will significantly advance our understanding of how humans use vision to control their movement through the natural world, which greatly increase our ability to develop clinical diagnosis and treatment for loss of locomotor function.